A community is either defined by a strongly shared belief or by the demographic if such a belief is absent. Hubski, as you have said is about much more than just deeper content. I saw that within 5 minutes of pitching up here.

People who do not share the mindset of the community could, with a big enough influx of similarly minded people, create a beachhead of sorts where they share content amongst themselves. In this regard Reddit is Hubski's biggest ally. It acts as a lighting rod for the content and user interaction that doesn't fit with Hubski. As long as Reddit provides an easier more accessible way to share funny cat pictures, those pictures will stay on Reddit as the majority of the existing Hubski community simply won't give it the traction it needs.

Now Hubski will fracture and develop subcultures as it grows and this is normal and not necessarily a bad thing, but in order to completely upset the apple cart it would require an influx of users that out number the existing community and that becomes less feasible as Hubski grows.

As long as Hubski as a community takes the time to teach and foster a vision amongst its new users there is no reason to fear its future. The day you have to rely on tools, rules and restrictions to manage the community you have already lost.

As long as Hubski wants to remain Hubski it will.

Edit: I forgot to mention that I am one of the new blood.